A Reasonable Price for Magic Plants

[Maat Mons]

If you're familiar with Pathfinder's magic plants, you know that the pricing formula makes them, arguably 16 times as expensive as they should be.

But what exactly should the pricing formula be? To a large extent, magic plants work like immobile items that duplicate a certain spell some number of times per day. But they actually do have a bit of an advantage over traditional items, they can "save up" charges.

Usually, if you have a 1/day item, and you don't use it for a few days, those charges from the days you skipped are wasted. But wont of the magic plants that regenerate one "charge" per day can store up to 7 days worth of "charges."

So what's a fair pricing formula for that? It would need to take into account charges regenerated each day, but also max charges stored. Any ideas?

[Morphic tide]

We could go for a setup that reduces the surcharge for each added day stored, as you have less and less reason to expect it to reach its maximum. A massive markup (over 120%!) for a worse product is simply nonsensical.

Something like a 50% additional cost per charge generated per day, then two days storage for a 50% overall markup, three days for an additive 40%, five for 30%, six for 20%, and seven and onwards are 10% each.

This would have a storage of two days be 2.25x base cost, six days would be 3.6x, and each day past that would be 15%. So the existing week of 1/day charges would cost ~46.6% less than the equivalent daily items.

[Maat Mons]

Thinking about it, as the charges recovered per day approach zero, the item approaches being an immobile stash of potions. So the formula should, in that case, approach max charges * 50 * spell lvl * caster lvl / 4.

And as the max number of charges stored approaches being equal to the number of charges regenerated each day, the item approaches being an ordinary immovable uses/day item. So, in that case, the formula should approach charges per day * 2,000 * spell lvl * caster lvl / 4.

The simplest formula I can think of that does that is:
[ (max charges - charges per day) * 12.5 * spell lvl * caster lvl ] + [ charges per day * 500 * spell lvl * caster lvl ]

But that formula doesn't seem to reflect any synergy between charges recovered per day and maximum number of charges stored. And it seems like some should exist. That suggests there should be a max charges * charges per day term. Or more precisely, and (max charges - charges per day) * charges per day term, so it zeroes out in the edge cases.

Then again, the formulas I've just described only really make sense when evaluating the value of a plant which the party finds fully charged. and you made a good point about that being increasingly unlikely as the time taken to reach full charge increases.

Maybe all the formulas I wrote should replace all the max charges - charges per day terms with some function that initially approximates that, but approaches some finite value as the ration of max charges / charges per day becomes large?

[Maat Mons]

Anyone have more to say on pricing?

Also, here are a bunch of poorly-though-out ideas for specific magic plants:

Antimagic Plant

constant Antimagic Field emanates from plant
fruit can be thrown to create area Dispel
fruit can be eaten for targeted dispel

Bacon Tree

grows crispy, fully-cooked bacon
magically remains fresh and unspoiled until picked

Black Apple

the first time a bite is taken out of this apple, it grants the eater a Wish
upon fulfilment of the Wish, the wisher loses 5,000 xp (or more)
this can result in level loss
if the wisher doesn't have 5,000 xp, they are reduced to zero xp and then die
nothing can prevent this xp loss (or the death)
someone slain in this way cannot be brought back by any means short of Wish or Miracle
creatures must have Int 3+ to make a wish
unintelligent creatures instinctively will not eat these apples

Blood Orange

Looks like an orange
Is actually full of blood
Blood stays magically fresh and uncoagulated until picked
Easy for vampire to bite “orange” and drink blood without spilling

Corpse Flower

large flower contains full-sized humanoid "corpse" curled in fetal position
"corpse" is gender-neutral, bald, and nondescript
"corpse" isn't subject to rot or decay until removed from flower
can be used as food for undead that require humanoid flesh
if "corpse" is animated, treat as human Commoner with average ability scores

Drizzling Willow

connected to elemental plane of water
constantly draws water from that plane
water drips from leaves, resulting in constant "rain" beneath tree

Foggy Fern

constantly emits fog cloud

Ghost Fruit

fruit is solid to incorporeal/ethereal creatures
ghosts et al. can eat fruit to temporarily become corporeal
fruit can be uses as thrown weapon to turn creature corporeal for shorter duration
wood from tree can be used to build objects and structures solid to incorporeal/ethereal creatures

Glow Fruit

fruit glows
glows continuously when attached to tree
after being removed from tree, fruit/juice continues to glow for some time
star-shaped?
twinkles?

Golden Apple

grants Miracle
can't do things that require xp

Insanity Peppers

very spicy peppers
eating them forces a save vs confusion
a delicious sauce can be made from them with even higher DC and longer duration

Invisible Tree

tree is invisible
if you can find and eat the fruit, you too become invisible temporarily
your clothing/gear doesn't turn invisible

Petrified Tree

tree, leaves, and fruit are made of stone
still grows somehow
if you somehow manage to eat fruit (literally hard as a rock) you too turn to stone

Poison Briar

briar is difficult terrain
creatures moving through take damage
damaged creatures must save against poison
often planted as defensive perimeter

Power Flower

???

Sanguine Rose

flower is ordinarily white
if someone is pricked by thorn, wound does not bleed, but rose turns red
rose then remains red for one month
if woman is pricked, she doesn't have her period that month
this incidentally prevent pregnancy
but more importantly, no cramps, and doesn't need pad

Seedless Grapes

when eaten by a man, causes him to become immediately (but temporarily) infertile
if dried, retain potency (at removing potency) indefinitely

Sleepy Grass

those walking through grass must save or become overwhelmingly tired
animals, elves, magical beasts, and fey are immune
creatures that fall asleep in grass will sleep infinitely unless something awakens them, or they are carried away from grass
creatures removed from grass continue sleeping for several hours unless roused
used by many elves as nonlethal fortification

Softstone Plant

turns rock into mud, then grows in mud

Sunflower

radiates light as bright as day
harms undead and such as if true daylight
light nourishes plants
grows parasitically symbiotically, like holly

Vermin Bane

plant constantly repels vermin

Zappy Plant

electrocutes those who touch it
must recharge between shocks


remove disease
remove curse
break enchantment
dimensional anchor/lock
hallow
mage's private sanctum
animal growth
regenerate
heal